1. Field of the Invention
The present disclosure relates to airflow modification. More particularly, illustrative embodiments relate to apparatus and methods for modifying aircraft cabin airflow. Other illustrative embodiments may relate to apparatus and methods for modifying airflow in other types of public transportation vehicles such as trains or buses, or in other enclosed spaces such as waiting rooms.
2. Description of the Related Art
Modern aircraft present a highly vulnerable environment for the transmission of airborne pathogens and disease. Particularly in light of recent Influenza and SARS epidemics, the current aircraft cabin environment causes concern for billions of air travelers worldwide, a figure predicted by the CDC to double within 20 years.[1] Isolated air in densely packed aircraft cabins serves as a vector for disease transmission via direct airborne and large droplet routes. Empirical investigations have consistently identified statistically significant correlations between disease contraction and air travel,[2, 3, 4] and government health researchers have marked the airplane cabin as especially vulnerable to transmitting tuberculosis, meningococcal disease, measles, and influenza.[5] Worsening matters, infected passengers incur widespread societal fear and large socioeconomic costs in providing treatment[6] and conducting contact tracing.[7]
Although most modern aircraft cabins are typically equipped with HEPA filters that are effective at removing over 99% of airborne pathogens, contaminated air must first be removed efficiently from the cabin to pass through these filters for pathogens to be removed. When a passenger sneezes in a conventional commercial aircraft cabin, mixing airflow patterns propagate the spread of pathogens throughout the cabin section,[8] causing pathogens to be inhaled by numerous other passengers before the contaminated air can be removed through outlet vents for cleaning by the HEPA cabin air filters of the Aircraft Environmental Control System for filtration and recirculation. Thus, for example, a single air passenger sick with the SARS virus was determined to have spread the virus to 22 other passengers on a single flight.[9]
Although some solutions to this problem have been proposed, they have not thus far proven to be viable.
For example, U.S. Pat. No. 6,910,961 to Niu discloses a personalized ventilation system integrated with a chair, for use in conjunction with building or vehicle ventilation systems. The chair has tubes and a nozzle configured to release air from the ventilation system very close to the nose and mouth of a person in the chair to prevent mixing with ambient air and to maximize the cooling and refreshing effect of the incoming conditioned air. However, this solution does not appear to be economically viable, as it would require a complete overhaul of the aircraft cabin interior, including the removal and replacement of all passenger seats and the installation of appropriate conduits to connect each seat to the aircraft's ventilation system. Such an extensive overhaul would require the aircraft to be taken out of service for months, resulting in too much lost revenue to permit an airline to adopt such a solution. This solution also presents ergonomic and aesthetic challenges for passengers, as the fresh air tubing placed in close proximity to the passenger's nose and mouth may hinder passenger comfort, and presents a risk of injury if the aircraft experiences turbulence or if the client moves suddenly after forgetting that an air intake tube is right beside their head.
As a further example, an under-floor displacement air distribution system has also been studied, involving the unconventional placement of some outlets at the top of the aircraft cabin and some inlets at the bottom of the cabin to produce a predominantly upward airflow, which is opposite to the generally downward airflow in conventional cabins which typically have outlets only near the floor and inlets only near the ceiling.[10] Such a system could, in theory, use human thermal plumes to expedite air exchange. However, it was concluded that the under-floor displacement air distribution system was not as effective at removing pathogens as a personalized ventilation system. Moreover, the under-floor displacement air distribution system is also economically unviable, requiring the aircraft to be taken out of service for potentially 1-2 months to install appropriate air ducting. In addition, inverting the airflow direction in this manner tends to present more unpleasant smells to passengers, such as foot odor and flatulence, for example.
Overhead gasper valves, although perhaps capable of supplying some additional fresh air to passengers, have not generally been effective in reducing pathogen propagation, and are commonly now offered only as an option, rather than a standard feature, to airlines purchasing newly manufactured aircraft.
Although the above discussion focuses on aircraft, other types of public transportation vehicles such as trains and buses for example, or other enclosed spaces, may also suffer from similar pathogen transmission problems.